An EEG test could one day be used to identify people at risk of developing mental illnesses such as schizophrenia before they show any symptoms.
Scientists have found that a type of EEG (electroencephalography) brain wave is slightly different in people who have siblings with schizophrenia, compared with that seen in the general population. The researchers believe the information could be used to identify those at highest risk and pre-emptively treat them before they develop a full-blown mental disorder.
"Unlike in general medicine where we have lots of reliable [biological] markers, such as blood sugar for diabetes, in psychiatry we still rely very much on the behaviours and symptoms a person reports when they go to see a clinician," said Maddie Groom of the University of Nottingham, who led the work.
She said markers of mental illness would not only help predict who was likely to be at risk but also how severe someone's condition is and how well they are responding to medication. "[Markers] would give us a really big handle not only on what's causing the disorder but also how best to treat and diagnose it," she said.
In her study, she took EEG recordings from 30 teenagers whose siblings had developed schizophrenia and compared these with EEGs from 36 controls. Schizophrenia is thought to be at least partly inherited, so the siblings of people who have the condition have a slightly increased risk of also developing the disorder.
"Their risk is still very small but, nonetheless, when you compare them with people with siblings who don't have schizophrenia, their risk is still greater than in the general population," said Groom.
The volunteers were asked to perform a task where they had to press a button every time they saw a particular image on a computer screen. They then had to inhibit that response and not press the button when a different stimulus appeared on the screen in its place.
"This is a really difficult test to do and people without any mental health problems find it difficult," said Groom. "But when we measured the brain activity of the siblings of the people with schizophrenia, their brain activity was reduced at the time when they needed to pay attention towards the stimulus and also when they needed to inhibit their response to that stimulus."
While they performed the task, a particular electrical signal known as the P300 wave was significantly reduced in the siblings of schizophrenia patients and in the patients themselves whenever the stimulus they had to ignore appeared on the screen.
The p300 marker is thought to reflect attentional and inhibitory control aspects of brain processing. When someone needs to focus on something that is particularly important, and when that something requires an inhibition of a motor response, the P300 marker tends to be larger in people with good mental health.
However, Groom stressed that the brain activity of the siblings was not radically different from healthy people and that the marker may be related to the risk of the disorder rather than the disorder itself.
"The difference on a case-by-case basis from our healthy group was very small and you wouldn't be able to pick them out from a crowd, measure their P300 and say that this person is related to someone with schizophrenia," said Groom.
The researchers are also investigating P300 in people with ADHD (attention deficit hyperactivity disorder). Groom presented her work today at the Forum of European Neuroscience (Fens) conference in Amsterdam.
Barbara Sahakian, a professor of clinical neuropsychology at the University of Cambridge, said: "If we could identify [people at risk of mental disorders] early with biomarkers and treat them early, we could probably get in there before any damage is done and they become relapsing and chronic."
In a separate study, also presented today at Fens, Seth Grant of the Wellcome Trust Sanger Institute in Cambridge created a catalogue that linked brain disorders to malfunctions in genes involved in making synapses, the junctions between nerve cells.
"What we found, in terms of disease, was quite striking – defects in the genes that encode these human synapse proteins are really a major cause of disease," he said. "There are over 135 nervous system diseases, psychiatric and neurological, that arise because of defects in these synaptic proteins. These are common and rare diseases – schizophrenia, bipolar disorder, autism."
He added: "We recognise that these synapse proteins are the molecular basis for many brain diseases. We know no other molecular structure that is responsible for more brain diseases ... Clinically, there is a wide spectrum of brain diseases and it is unclear how some of those are related to one another and if they are related at all. We can now see that many of them are related to one another because the molecular underpinnings of those diseases are in the synapse proteins which are physically binding to one another. There is a unifying mechanism that underpins a large number of brain diseases."
The findings will help target drugs for mental conditions more accurately in future, said the scientists. When the synapses and their role in disease are fully understood, said Grant, scientists will have scores of new targets to develop drugs against. In addition, a drug would no longer be used to treat, say, only schizophrenia or autism, but would instead treat individual characteristics related to the malfunction of particular genes, which might be common to several diseases.
